1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device. More particularly, the invention relates to a method of introducing a conductivity modifying dopant into a semiconductor material. Most particularly, the invention relates to proton beam transmutation doping.
2. Discussion of the Related Art
Wide band gap semiconductor materials such as diamond, SiC, AlN, AlGaN, GaN, GaP, Al2O3 and AlAs are of continuing interest for use in semiconductor products. However, their full potential has not been realized because of the difficulty in doping to activate them for use.
Conventional methods of doping methods, such as ion implantation and thermal diffusion are difficult to implement in wide band gap materials because of the rigid, high strength lattice structure. The lattice structure reduces the replacement of lattice atoms with dopant atoms to a small fraction. In the case of interstitial doping, the substrate suffers significant damage. Annealing is required to heal the damage, resulting in migration and loss of interstitial dopant atoms. Substitution doping is preferred over interstitial doping for electrical reliability of the semiconductor over time and over a temperature range.
Neutron transmutation doping (NTD) creates radioactive species which must be isolated until the induced radioactivity diminishes to safe levels. Also, neutrons are extremely penetrating and electrically neutral, so neutron transmutation doping dopes the entire lattice by using neutrons of varying energies.
Chemical vapor deposition (CVD) may be applied for doping wide band gap materials. However, the control of gas, chemical reactions and incorporation into the lattice limits the doping layer thickness and quality.
These methods have been tried for creating p-type boron doped diamond. One of the outstanding challenges in doping wide band gap materials is the creation of n-type diamond. Diamond has excellent properties including high breakdown voltage, high electron and hole mobility and high thermal conductivity. These properties indicate that it has potential for use in semiconductor applications.
These and other problems of doping high band gap semiconductor materials are solved, at least in part, by the proton beam transmutation doping method of the invention.